Many different pieces of machinery and other devices include internal surfaces or bores that need to be made to some precise diameter. Such bores are often finished and brought to the desired size or diameter by a honing operation, and in these and other cases, there exists a need to provide very accurate gaging means which are able to quickly and accurately determine if the diameter and surface characteristics are of the desired size and finish or if the diameter is off by some amount, and if so, whether the bore is over or under size. For example, a person drilling, cutting or honing a hole or bore in a particular workpiece will normally perform frequent precise measurements of the bore diameter to ensure that the finished diameter corresponds to that required. Many different types of gaging devices including a wide variety of dial bore gages have been constructed and used in the past to accomplish this end. Dial bore gages are specifically used to determine if the diameter and surface characteristics of cylindrical holes or bores are accurate to some known standard and such gages include gaging head members which engage the surfaces which are to be gaged and have portions operatively connected to dial indicator means which indicate the condition and size of the hole or bore. Typical of the known dial bore gaging devices are those shown and disclosed in U.S. Pat. Nos. 2,968,102; 4,045,877; 4,170,831; 4,227,310; 4,419,829 and 4,419,830.
All known prior art dial bore gages have certain shortcomings, limitations, and disadvantages which have either limited or restricted their usefulness or have greatly affected the accuracy of such devices or have rendered such devices unreliable. For example, many of the known gaging devices are relatively complicated structurally and include complicated work engaging portions. Many of the same devices also include complicated gage centralizing mechanisms for ensuring that the gaging members are located on a diameter of the work surface to be gaged including centralizer mechanisms that are primarily associated with one gaging contact only, usually the movable contact. In addition, the known gaging devices are constructed such that movement of the centralizing members is controlled by a mechanism which is independent from the mechanism controlling movement of the movable gaging member that actually does the gaging. All of these features of the known dial bore gages including especially their work engaging portions have resulted in work engaging portions that are relatively complex, expensive to manufacture, difficult and cumbersome to assemble, disassemble and repair, and the known gage head assemblies have included a relatively large number of parts and/or components all of which have placed severe limitations on them as to the smallness of size and the diameter of bores that can be gaged. As a result, many of the known prior art gaging devices, because of their relatively large size, cannot be made to be inserted into relatively small diameter bores. Furthermore, the known devices have not provided means for prolonging the life of the gage by making the work engaging elements removable, replaceable and interchangeable. Also none of the known gaging heads uses as simple a centralizing means as the present constructions and none utilize a mechanism wherein both the gaging members and the centralizing members are simultaneously movable radially, the gaging members being positioned radially outward slightly further than the centralizing members in all positions of adjustment In addition, the present gaging head constructions are designed to be quickly and easily installed on a gage and placed in operating condition, they are capable of being adjusted to extreme accuracy and close tolerances, and they can be made in a wide variety of sizes including especially in sizes to cover relatively small bore diameters, and all of the different head sizes can be installed for use on the same or similar type gaging devices such as on known dial bore gages.